Polythiophenes have been studied extensively due to their interesting electrical and/or optical properties. Polythiophenes become electrically conducting upon chemical or electrochemical oxidation or reduction.
EP-A 257 573 discloses an intrinsically electrically conductive polymer, wherein through connection in the 2-position and/or the 5-position are coupled to one another, statistically averaged from 60 to 100% by weight structural units, which are derived from at least one monomer of the formula (1): in which R1 is a C1-2-alkoxy group or —O(CH2CH2O)nCH3 with n=1 to 4 and R2 is a hydrogen atom, a C1-12-alkyl group, a C1-12-alkoxy group or —O(CH2CH2O)nCH3 with n=1 to 4, or R1 and R2 together are —O(CH2)m—CH2— or —O(CH2)m—O— with m=1 to 12, 0 to 40% by weight structural units, which are derived from at least one monomer of the formula (2): wherein R4 and R5 are independently of one another a hydrogen atom, a halogen atom, a C1-12-alkyl group or aryl or together with C-atoms connected to them form an aromatic ring, R3 and R6 independently of one another represent a hydrogen atom or R3 together with R4 and the C-atoms connected to them or R5 together with R6 and the C-atoms connected to them each form an aromatic ring, X represents an oxygen atom, a sulphur atom, a ═NH group, a ═N-alkyl group or a ═N-aryl group, 0 to 40% by weight structural units, which are derived from at least one monomer of formula (3): where R7, R8, R9 and R10 independently of one another represent a hydrogen atom, a C1-12-alkyl group, a C1-12-alkoxy group or an aryl group, Y and Z independently of one another represent an oxygen is atom, a sulfur atom, a ═NH group, a ═N-alkyl group or a ═N-aryl group, R11 represents an arylene group, a heteroarylene group or a conjugated system of the formula (CH═CH)o, wherein o is 1, 2 or 3, 0 to 40& by weight structural units, which are derived from at least one monomer of formula (4): wherein R12 and R13 independently of one another represent a hydrogen atom, a halogen atom, a C1-12-alkyl group, a C1-12-alkoxy group, a C1-4-alkylamino group or a C1-4-acylamino group, R14 represents a halogen atom, a C1-12-alkyl group, a C1-12-alkoxy group, a C1-4-alkylamino group or a C1-4-acylamino group and X has the meaning given above, wherein the polymer in the oxidized form is completely soluble in dipolar aprotic solvents at 25° C. and solutions with a content of at least 0.1 g of the polymer in 100 mL solvent at 25° C. are obtained.
EP-A 339 340 discloses a polythiophene containing structural units of the formula: in which A denotes an optionally substituted C1-4-alkylene radical and its preparation by oxidative polymerization of the corresponding thiophene.
EP-A 440 957 discloses dispersions of polythiophenes, constructed from structural units of formula (I): in which R1 and R2 independently of one another represent hydrogen or a C1-4-alkyl group or together form an optionally substituted C1-4-alkylene residue, in the presence of polyanions. In Example 3 air is bubbled through the polymerizing solution.
Furthermore, Walsh et al. in 1999 in Macromolecules, volume 32, pages 2397-2399 reported the preparation of 3-substituted heteroaryl polythiophene by chemical polymerization using 4 molar equivalents of FeCl3 in chloroform at 50° C. under a slow purge of dry air; and Pomerantz et al. in 1991 in Synthetic Metals, volumes 41-43, pages 825-830 reported the preparation of poly(3-alkylthiophenes) using anhydrous FeCl3 in chloroform while dry air was bubbled through the reaction mixture.
However, electropolymerization of polymers, such as polymers of 5-membered heterocyclic compounds containing 1 atom of an element from the O or N group, is classically carried out under a blanket of inert gas, see, for example, JP 59-210947 and Zhang et al. in 2001 in Journal of Solid State Electrochemistry, volume 5, pages 74-79.
A general drawback of conductive polymers which have been prepared and studied up to now, is that their conductivities are still too low for certain applications, their visible light transmittances are insufficiently high, their stability to visible and UV light exposure is too low and/or they are not processable.